Pressure sensors are widely used in multiple applications, such as automotive applications, medical diagnostics, altitude and depth measurements and flow sensing.
Use of opto-mechanical pressure sensors has recently become focus of increasing attention. Sensors based on opto-mechanical solutions may provide a high sensitivity in combination with a low noise level, which makes opto-mechanical pressure sensors interesting in relation to pressure sensors based on piezoelectric or capacitive technology.
An opto-mechanical pressure sensor may be based on a Mach Zehnder-type interferometer (MZI) device, wherein light is split into two paths. One of the paths, a measurement path, is subject to a pressure affecting light propagation through the path, whereas the other path, a reference path, works as a fixed reference. The light from the measurement and reference paths is then recombined and an optical intensity output from the MZI device is dependent on the phase difference of light between the two paths and, thus, on the pressure the measurement path is subject to.
The intensity of light output by the MZI device may thus be used for measuring a pressure with a high sensitivity. However, a range of sensitivity of the MZI device is limited by the phase shift caused by the pressure to which the measurement path is subject to. Thus, if the phase shift is above π radians, it is not possible to differentiate the intensity output from the MZI from a phase shift below π radians. Hence, a sensitivity range of the MZI device is limited to phase shifts below π radians.
MZI devices may also be used for other types of sensing applications, not necessarily sensing a pressure. Rather, any external influence acting on the measurement path may be sensed, such as any type of force, e.g. caused by a pressure differential or by a direct force.